With the obesity epidemic permeating all segments of society, novel weight loss tools with broad appeal and reach are essential. The pervasive use of personal mobile phones in the U.S. provides a unique opportunity to promote positive behavior change through timely and tailored health messages. We propose to develop a mobile phone based application, Text4Diet", designed to produce and maintain weight loss through improved diet and physical activity (PA) behaviors. Text4Diet" will build upon a novel text-message-based intervention, mDIET (mobile Dietary Intervention through Electronic Technology), recently found efficacious for weight loss among overweight/obese adults in an NCI-funded randomized controlled trial (R21 CA115615- 01A1;K Patrick, PI). To our knowledge the mDIET study is the first to produce evidence of the efficacy of text messages to promote weight loss among overweight/obese adults. The Text4Diet" system will embed the core mDIET technology into a larger web platform that supports commercialization. This includes initial web-based dietary and physical activity assessment to identify behaviors to target with tailored text and MMS (graphical and picture) messages. Text4Diet" then allows users to self-monitor weight;improve nutrition behaviors, such as increasing consumption of fiber, fruits and vegetables, decreasing consumption of dietary fat, and consuming appropriate portion sizes;improve PA behaviors;record and track step counts;and receive timely text message prompts and suggestions to serve as positive reminders and motivators for achieving their behavior change goals. Users also have access to an extensive online library containing nutrition and PA information and strategies to supplement the Text4Diet" mobile application. Text4Diet will be evaluated in a 9 month randomized controlled trial among overweight and obese (BMI of 25.0 to 39.9) men and women, aged 21- 65. The primary outcome will be change in weight (kg) at 6 months. Secondary outcomes include: change in weight at 9 months, change in pedometer step counts, satisfaction with the Text4Diet" application, adherence to the intervention, eating behaviors and physical activity behaviors. Phase I activities will include: a) development of the Text4Diet" website supporting user enrollment and diet and physical activity assessment;b) automation of the administration and scoring of the diet and PA assessments;c) at least 500 new text and MMS messages addressing additional behaviors;d) expansion of the expert logic system to respond dynamically to a user's progress;e) inclusion of pedometer data into the text message logic, f) new software to produce step count graphs, g) completion of alpha system testing, and h) completion of usability testing of enrollment system. In Phase II, a 2 month beta test will be completed to evaluate the expanded Text4Diet" application developed during Phase I. The beta test results will be incorporated into the final system tested in the 9 month randomized controlled trial. Measurement will take place at 0, 6 and 9 months. PUBLIC HEALTH RELEVANCE: Given the increasing prevalence of overweight and obesity in the U.S., it is apparent that innovative and sophisticated weight loss tools are needed. Three-quarters of the U.S. population now carries a mobile phone. Text4Diet" will capitalize on this unique opportunity to facilitate weight loss and weight loss maintenance through the delivery of personalized and timely behavioral text messages.